Study

Understanding the release efficiency of Atlantic cod (Gadus morhua) from trawls with a square mesh panel: effects of panel area, panel position, and stimulation of escape response

  • Published source details Herrmann B., Wienbeck H., Karlsen J.D., Stepputtis D., Dahm E. & Moderhak W. (2015) Understanding the release efficiency of Atlantic cod (Gadus morhua) from trawls with a square mesh panel: effects of panel area, panel position, and stimulation of escape response. ICES Journal of Marine Science, 72, 686-696

Actions

This study is summarised as evidence for the following.

Action Category

Fit a moving device to a trawl net to stimulate fish escape response (stimulator device)

Action Link
Marine Fish Conservation

Modify the configuration of a mesh escape panel/window in a trawl net

Action Link
Marine Fish Conservation
  1. Fit a moving device to a trawl net to stimulate fish escape response (stimulator device)

    A replicated, controlled study in 2012 of a seabed area in the Arkona Basin, western Baltic Sea, Northern Europe (Herrmann et al. 2015) found that only one of three designs of moving devices to stimulate fish escape response (active stimulating devices) fitted to trawl net codends in tandem with a square mesh escape panel improved the size selectivity of cod Gadus morhua compared to a codend without a device. The length at which cod had a 50% chance of escaping (selection length) was greater with float ropes as the stimulating device, for two different sizes of catch (200 kg: 36.7 cm, 700 kg: 38.3 cm) compared to the two other devices (fluttering rope and inclined panel) and without a device, which did not differ from each other (200 kg: 29.5 cm, 700 kg: 31.0 cm). Experimental fishing trials were done in March/April and September 2012. Deployments were made of four identical codends with a 120 mm top square mesh escape panel in the front of the codend and with or without an active stimulating device. Three codends with devices were tested: fluttering ropes (8 tows), an inclined panel (5 tows) and float ropes (3 tows), and one without (11 tows). See paper for gear specifications. A cover mounted over each codend collected the escaping cod. Catches from both codends and covers were sorted, and cod length and number recorded.

    (Summarised by: Natasha Taylor)

  2. Modify the configuration of a mesh escape panel/window in a trawl net

    A replicated, controlled study in 2012 of a seabed area in the western Baltic Sea, northern Europe (Herrmann et al. 2015) found that changing the size and position of a square mesh escape panel in the codend of a trawl net did not increase the likelihood of escape of small Atlantic cod Gadus morhua, compared to a standard trawl design with a square mesh panel codend (Bacoma). The length at which cod had a 50% chance of escape was similar in codends with small square mesh panels located either towards the back (30.2–40.3 cm) of the codend or at the front of the codend (30.6–41.7 cm), compared to the standard large square mesh panel codend (35.2–41.8 cm). For three of the four codends with the small square mesh panel at the front, the length at which cod had a 50% chance of escaping was smaller (21.3–41.7 cm) (two codends not tested for significance). Trials were conducted in March/April and September 2012 in the Arkona Basin. A total of 41 alternate haul deployments were done with six separate codends, comprising different combinations of size/position of square mesh panel, one of them the established Bacoma design, the other five with a 50% smaller square mesh panel, four of which had the panel at the front of the codend. A cover was applied to each codend to retain and sample escaped cod. Full gear specifications are given in the original paper. Catches from both the codends and the covers were sorted, and all cod counted and lengths measured.

    (Summarised by: Natasha Taylor)

Output references

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